1. Field of the Invention
The present invention relates to an image reading apparatus, and more specifically relates to an image reading apparatus for reading images recorded on light-transmitting film by means of a linear sensor array.
2. Description of the Related Art
Conventional image reading apparatus using a linear sensor array comprising a plurality of reading elements disposed in a single row typically illuminate a film by means of light emitted from a light source unit, and irradiate a linear sensor array via a projection lens by means of the light transmitted through said film. A single image of the film is read by moving the film at a predetermined speed in a subscanning direction which is perpendicular to a main scanning direction which is the direction of the array of aligned reading elements. A Kohler illumination system capable of illuminating a film of broad area regardless of the shape and size of the light source may be used as the aforesaid illumination system.
There are a plurality of film sizes including 4.times.5 inch format, Brownie format, 35 mm format and the like. Whatever the film size, in order to read an image at high resolution, the projection magnification must be changed in accordance with said film size, such that an image is typically displayed in the entire main scanning direction of the linear sensor array. In a conventional image reading apparatus, the aforesaid change of the projection magnification is accomplished by a method wherein the lens is replaced by another lens having a different focal length, or a method wherein the focal length of a zoom lens is changed while said lens is stationary at a predetermined position.
Methods for changing projection magnification in conventional apparatus can satisfy the requirements of Kohler illumination without moving the illumination unit because the lens pupil movement is quite small. In the case of the lens replacement method the disadvantage is that the lens must be replaced for each film size, and when a zoom lens is used, the disadvantage is that the number of lenses increases and the lens diameter increases, thereby greatly enlarging the lens system.
In conventional image reading apparatus, the image scan in the subscanning direction is accomplished by moving the film. However, methods for moving the film require that the film loading device is exposed outside the apparatus to facilitate the film replacement operation, and there is some danger that the hand of an operator may inadvertently come into contact with the moving portion.